Well cement additives, compositions and methods

ABSTRACT

Improved well cement additives, compositions and methods of using the compositions are provided. The well cement additives are basically comprised of a first monomer selected from the group of 2-acrylamido-2-methylpropane sulfonic acid, 2-allyloxy-2-hydroxy-1-propane sulfonic acid and vinylsulfonic acid, a second monomer selected from the group of N,N-dimethylacrylamide, acrylamide, N-vinylpyrrolidone, N-vinylacetamide and acrylonitrile and a third monomer selected from the group of C 6  to C 22  dimethylaminopropylmethacrylamide bromide, chloride and iodide and C 6  to C 22  dimethylaminoethylmethacrylate bromide, chloride and iodide.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This is a divisional of application Ser. No. 09/988,970 filed onNov. 19, 2001, now pending.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to subterranean well cementingoperations, and more particularly, to improved well cement compositionfluid loss control additives, well cement compositions containing theadditives and methods of using the compositions.

[0004] 2. Description of the Prior Art

[0005] Hydraulic cement compositions are commonly utilized insubterranean well completion and remedial operations. For example,hydraulic cement compositions are used in primary cementing operationswhereby strings of pipe such as casings and liners are cemented in wellbores. In performing primary cementing, a hydraulic cement compositionis pumped into the annular space between the walls of a well bore andthe exterior surfaces of a pipe string disposed therein. The cementcomposition is permitted to set in the annular space thereby forming anannular sheath of hardened substantially impermeable cement thereinwhich supports and positions the pipe string in the well bore and bondsthe exterior surfaces of the pipe string to the walls of the well bore.Hydraulic cement compositions are also utilized in remedial cementingoperations such as plugging highly permeable zones or fractures in wellbores, plugging cracks or holes in pipe strings and the like.

[0006] Fluid loss control agents are used in well cement compositions toreduce fluid loss from the cement compositions to permeable formationsor zones into or through which the cement compositions are pumped. Inprimary cementing, the loss of fluid, i.e., water, to permeablesubterranean formations or zones can result in premature gelation of thecement compositions whereby bridging of the annular space between thepermeable formation or zone and the pipe string being cemented preventsthe cement compositions from being placed over the entire length of theannulus. A number of fluid loss control additives have been utilized inwell cement compositions heretofore. A particularly useful cementcomposition fluid loss control additive is described in U.S. Pat. No.4,555,269 issued to Rao et al. on Nov. 26, 1985 which is assigned to theassignee of this present invention. The fluid loss control additive iscomprised of copolymers and copolymer salts of N,N-dimethylacrylamideand 2-acrylamido-2-methylpropane sulfonic acid having molecular weightsof between about 75,000 and 300,000.

[0007] While the above well cement composition fluid loss controladditive and other heretofore known fluid loss control additives havefunctioned successfully, there are continuing needs for improved wellcement composition fluid loss control additives which bring about lessfluid loss while maintaining static cement gel strength properties, wellcement compositions including the additives and methods of using thecompositions.

SUMMARY OF THE INVENTION

[0008] The present invention provides well cement composition fluid losscontrol additives, well cement compositions including the additives andmethods of using the compositions which meet the needs described aboveand overcome the deficiencies of the prior art. The improved well cementcomposition fluid loss control additives are comprised of terpolymershaving molecular weights in the range of from about 75,000 to about300,000. The terpolymers are comprised of first, second and thirdmonomers wherein the first monomer is selected from the group of2-acrylamido-2-methylpropane sulfonic acid,2-allyloxy-2-hydroxy-1-propane sulfonic acid and vinylsulfonic acid, thesecond monomer is selected from the group of N,N-dimethylacrylamide,acrylamide, N-vinylpyrrolidone, N-vinylacetamide and acrylonitrile andthe third monomer is selected from the group of C₆ to C₂₂dimethylaminopropylmethacrylamide bromide, chloride and iodide and C₆ toC₂₂ dimethylaminoethylmethacrylate bromide, chloride and iodide. Apreferred such fluid loss control additive is comprised of a terpolymerof 2-acrylamido-2-methylpropane sulfonic acid, N,N-dimethylacrylamideand hexadecyldimethylaminopropylmethacrylamide bromide.

[0009] The improved cement compositions of this invention are basicallycomprised of a hydraulic cement, sufficient water to form a slurry and aterpolymer fluid loss control additive of this invention.

[0010] The methods of this invention for cementing a zone in asubterranean formation penetrated by a well bore are basically comprisedof the steps of providing a cement composition of this invention asdescribed above, placing the cement composition in the zone to becemented and allowing the cement composition to set into an impermeablesolid mass therein.

[0011] It is, therefore, an object of this invention to provide improvedwell cement fluid loss control additives, cement compositions containingthe additives and methods of using the compositions.

[0012] Other and further objects, features and advantages of the presentinvention will be readily apparent to those skilled in the art upon areading of the description of preferred embodiments which follows.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0013] The improved fluid loss control additives for use in the wellcement compositions of this invention are basically comprised ofterpolymers having molecular weights in the range of from about 75,000to about 300,000. An example of a particularly preferred well cementfluid loss control additive is a terpolymer comprised of2-acrylamido-2-methylpropane sulfonic acid, N,N-dimethylacrylamide andhexadecyldimethylaminopropylmethacrylamide bromide, chloride or iodide.This fluid loss control additive provides superior reductions in fluidloss from well cement compositions without compromising the static gelstrength properties of the cement compositions during setting. While thehexadecyl dimethylammonium propylmethacrylamide bromide monomer adds ahydrophobic hydrocarbon chain having 16 carbon atoms to the terpolymer,the monomer has an ionic charge that gives it water solubility. Inaddition, the monomer gives the terpolymer unique associative propertieswhich provide increased effectiveness to the terpolymer as a well cementcomposition fluid loss control additive and, as mentioned, providesincreased static cement gel strength properties to the cementcomposition. Since the hexadecyl dimethylammonium propylmethacrylamidebromide monomer is water soluble, the terpolymer can be synthesized inan aqueous solution. The terpolymer can also be made in the form of anemulsion.

[0014] The hexadecyldimethylaminopropylmethacrylamide bromide, chlorideor iodide monomer which is utilized to form the fluid loss controladditive terpolymer can be prepared by adding an equi-molar mixture ofdimethylaminopropylmethacrylamide and hexadecylbromide, chloride oriodide to a flask heated to 60° C. with stirring and held for 24 hours.To this mixture is added an appropriate solvent, such as petroleumether, which is miscible with the starting materials and willprecipitate the product monomer, i.e.,hexadecyldimethylaminopropylmethacrylamide bromide, chloride or iodide.The product can be collected on a Buchner funnel, washed with morepetroleum ether, dried, and used in subsequent polymerization reactions.

[0015] The terpolymer can be prepared by dissolving in water themonomers 2-acrylamido-2-methylpropane sulfonic acid (AMPS),N,N-dimethylacrylamide and hexadecyldimethylaminopropylmethacrylamide(C₁₆ DMAPMA) bromide, chloride or iodide in amounts to give a 10% activesolution. To this solution, an appropriate amount of polymerizationinitiator, such as 2,2′-azobis(2-amidinopropane) dihydrochloride, isadded. The solution is then heated to initiate polymerization and toform a solution of the terpolymer. The AMPS/NNDMA/C₁₆ DMAPMA bromide,chloride or iodide terpolymer preferably has an AMPS to NNDMA to C₁₆DMAPMA Br, Cl or I mole ratio of 59.5:39.5:1.

[0016] A preferred improved well cement composition of the presentinvention is basically comprised of a hydraulic cement, sufficient waterto form a slurry and a fluid loss control additive comprising aterpolymer of 2-acrylamido-2-methylpropane sulfonic acid,N,N-dimethylacrylamide and hexadecyldimethylaminopropylmethacrylamidebromide, chloride or iodide.

[0017] In addition to the monomers described above, various other first,second and third monomers can be utilized to form terpolymer fluid losscontrol additives of this invention. The monomers that can be utilizedto form the terpolymers of this invention and which provide improvedfluid loss control and static gel strength to well cement compositionsare set forth in Table I below. TABLE I Monomers For Forming TerpolymersOf The Present Invention First Monomers Second Monomers Third Monomers2-acrylamido-2- N,N-dimethylacrylamide C₆ to C₂₂ methylpropanedimethylaminopropyl- sulfonic acid methacrylamide bromide, chloride oriodide 2-allyloxy-2-hydroxy- Acrylamide 1-propane sulfonic acidvinylsulfonic acid N-vinylpyrrolidone C₆ to C₂₂ dimethylaminoethyl-methacrylate bromide, chloride or iodide N-vinyacetamide acrylomtrile

[0018] The terpolymers of the present invention that can be formed usingthe above monomers include, but are not limited to:2-acrylamido-2-methylpropane sulfonic acid/N,N-dimethylacrylamide/C₆-C₂₂dimethylaminopropylmethacrylamide bromide, chloride or iodide;2-acrylamido-2-methylpropane sulfonic acid/acrylamide/C₆-C₂₂dimethylaminopropylmethacrylamide bromide, chlorine or iodide;2-acrylamido-2-methylpropane sulfonic acid/N-vinylpyrrolidone/C₆-C₂₂dimethylaminopropylmethacrylamide bromide, chloride or iodide;2-acrylamido-2-methylpropane sulfonic acid/N-vinylacetamide/C₆-C₂₂dimethylaminopropylmethacrylamide bromide, chloride or iodide;2-acrylamido-2-methylpropane sulfonic acid/acrylonitrile/C₆-C₂₂dimethylaminopropylmethacrylamide bromide, chloride or iodide;2-acrylamido-2-methylpropane sulfonic acid/N,N-dimethylacrylamide/C₆-C₂₂dimethylaminoethyl-methacrylate bromide, chloride or iodide;2-acrylamido-2-methylpropane sulfonic acid/acrylamide/C₆-C₂₂dimethylaminoethylmethacrylate bromide, chloride and iodide;2-acrylamido-2-methylpropane sulfonic acid/N-vinylpyrrrolidone/C₆-C₂₂dimethylaminoethylmethacrylate bromide, chloride or iodide;2-acrylamido-2-methylpropane sulfonic acid/N-vinylacetamide/C₆-C₂₂dimethylaminoethylmethacrylate bromide, chloride or iodide;2-acrylamido-2-methylpropane sulfonic acid/acrylonitrile/C₆-C₂₂dimethylaminoethylmethacrylate bromide, chloride and iodide;2-allyloxy-2-hydroxy-1-propane sulfonic acid/N,N-dimethylacrylamide/C₆to C₂₂ dimethylaminopropylmethacrylamide bromide, chloride or iodide;2-allyloxy-2-hydroxy-1-propane sulfonic acid/acrylamide/C₆ to C₂₂dimethylaminopropylmethacrylamide bromide, chloride or iodide;2-allyloxy-2-hydroxy-1-propane sulfonic acid/N-vinylpyrrolidone/C₆ toC₂₂ dimethylaminopropylmethacrylamide bromide, chloride or iodide;2-allyloxy-2-hydroxy-1-propane sulfonic acid/N-vinylacetamide/C₆ to C₂₂dimethylaminopropylmethacrylamide bromide, chloride or iodide;2-allyloxy-2-hydroxy-1-propane sulfonic acid/acrylonitrile/C₆ to C₂₂dimethylaminopropylmethacrylamide bromide, chloride or iodide;vinylphosphonic acid/N,N-dimethylacrylamide/C₆ to C₂₂dimethylaminopropylmethacrylamide bromide, chloride or iodide;vinylsulfonic acid/acrylamide/C₆ to C₂₂dimethylaminopropylmethacrylamide bromide, chloride or iodide;vinylsulfonic acid/N-vinylpyrrolidone/C₆ to C₂₂dimethylaminopropylmethacrylamide bromide, chloride or iodide;vinylsulfonic acid/N-vinylacetamide/C₆ to C₂₂dimethylaminopropylmethacrylamide bromide, chloride or iodide;vinylsulfonic acid/acrylonitrile/C₆ to C₂₂dimethylaminopropylmethacrylamide bromide, chloride or iodide;2-allyloxy-2-hydroxy-1-propane sulfonic acid/N,N-dimethylacrylamide/C₆to C₂₂ dimethylaminoethylmethacrylate bromide, chloride or iodide;2-allyloxy-2-hydroxy-1-propane sulfonic acid/acrylamide/C₆ to C₂₂dimethylaminoethylmethacrylate bromide, chloride or iodide;2-allyloxy-2-hydroxy-1-propane sulfonic acid/N-vinylpyrrolidone/C₆ toC₂₂ dimethylaminoethylmethacrylate bromide, chloride or iodide;2-allyloxy-2-hydroxy-1-propane sulfonic acid/N-vinylacetamide/C₆ to C₂₂dimethylaminoethylmethacrylate bromide, chloride or iodide;2-allyloxy-2-hydroxy-1-propane sulfonic acid/acrylonitrile/C₆ to C₂₂dimethylaminoethylmethacrylate bromide, chloride or iodide;vinylsulfonic acid/N,N-dimethylacrylamide/C₆ to C₂₂dimethylaminoethylmethacrylate bromide, chloride or iodide;vinylsulfonic acid/acrylamide/C₆ to C₂₂ dimethylaminoethylmethacrylatebromide, chloride or iodide; vinylsulfonic acid/N,N-vinylpyrrolidone/C₆to C₂₂ dimethylaminoethylmethacrylate bromide, chloride or iodide;vinylsulfonic acid/N-vinylacetamide/C₆ to C₂₂dimethylaminoethylmethacrylate bromide, chloride or iodide; andvinylsulfonic acid/acrylonitrile/C₆ to C₂₂dimethylaminoethylmethacrylate bromide, chloride or iodide.

[0019] The forgoing terpolymers can all be formed as described aboverelating to the most preferred terpolymer, i.e.,2-acrylamido-2-methylpropane sulfonic acid/N,N-dimethylacrylamide/C₁₆dimethylammonium propylmethacrylamide bromide.

[0020] A variety of hydraulic cements can be utilized in accordance withthe present invention including those comprised of calcium, aluminum,silicon, oxygen and/or sulfur which set and harden by reaction withwater. Such hydraulic cements include, but are not limited to, Portlandcements, pozzolana cements, gypsum cements, aluminous cements and silicacements. Portland cements are generally preferred for use in accordancewith the present invention, and Portland cements of the types definedand described in API Specification For Materials And Testing For WellCements, API Specification 10, 5^(th) Edition, dated Jul. 1, 1990 of theAmerican Petroleum Institute are particularly preferred. API Portlandcements include Classes A, B, C, G and H. API Classes G and H arepreferred with Class G being the most preferred.

[0021] The water utilized in the compositions of this invention can befresh water, unsaturated salt solutions and saturated salt solutions.Generally, the water can be from any source provided it does not containan excess of compounds that adversely affect other components in thecement compositions. The water is present in the cement compositions ofthis invention in an amount sufficient to form a pumpable slurry. Moreparticularly, the water is present in the cement compositions in anamount in the range of from about 37% to about 56% by weight ofhydraulic cement therein.

[0022] As mentioned above, the fluid loss control additive terpolymer ofthis invention is comprised of a first monomer, most preferably2-acrylamido-2-methylpropane sulfonic acid, a second monomer, mostpreferably N,N-dimethylacrylamide and a third monomer, most preferablyhexadecyldimethylaminopropylmethacrylamide bromide. As also mentioned, avariety of other first, second and third monomers can be utilizedincluding those listed above. Generally, the first monomer is present inthe terpolymer in an amount in the range of from about 50 to about 70mole percent, the second monomer is present in an amount in the range offrom about 30 to about 50 mole percent and the third monomer is presentin an amount in the range of from about 1 to about 10 mole percent. Morepreferably, the first monomer is present in the terpolymer in an amountin the range of from about 60 to about 70 mole percent, the secondmonomer is present in an amount in the range of from about 30 to about40 mole percent and the third monomer is present in an amount in therange of from about 1 to about 5 mole percent. Generally, the terpolymerhas a molecular weight in the range of from about 75,000 to about300,000, most preferably a molecular weight of about 250,000.

[0023] The terpolymer fluid loss control additive is generally presentin the well cement compositions of this invention in an amount in therange of from about 0.1% to about 2% by weight of hydraulic cementtherein. As will be understood by those skilled in the art, the wellcement compositions can include other conventional well cement additivessuch as set accelerating additives, set retarding additives, fillers,weighting materials, lightening materials and the like.

[0024] As will be understood by those skilled in the art, a variety ofconventional additives can be included in the cement compositions ofthis invention including, but not limited to, set retarders, setaccelerators, dispersants and lightweight additives such asmicrospheres, sodium silicate, bentonite and the like. When lightweightadditives are included, the amount of water required in the cementcompositions often increases.

[0025] The methods of the present invention for cementing a subterraneanzone penetrated by a well bore are basically comprised of the steps ofproviding a cement composition of this invention as described above,placing the cement composition in the zone to be cemented and allowingthe cement composition to set into an impermeable solid mass therein.

[0026] In order to further illustrate the cement compositions andmethods of the present invention, the following example is given.

EXAMPLE

[0027] A cement slurry comprised of Portland Class H cement and freshwater in an amount of 42% by weight of cement was prepared. The cementslurry was divided into eight samples. To four of the samples, varyingamounts of the above mentioned prior art fluid loss control additivecomprised of a co-polymer of 2-acrylamido-2-methylpropane sulfonic acidand N,N-dimethylacrylamide in emulsion form were added. The preferredterpolymer fluid loss control additive of the present invention, i.e., aterpolymer of 2-acrylamido-2-methylpropane sulfonicacid/N,N-dimethylacrylamide/hexadecyldimethylaminopropylmethacrylamidebromide was added to four additional samples of the cement slurry in thesame amounts as the prior art fluid loss control additive added to thefirst four cement slurry samples. A lignosulfonate set retardingadditive and sodium chloride salt were also added to some of the cementslurry test samples. The cement slurry samples were tested for fluidloss in accordance with the procedure described in the above mentionedAPI Specification 10 at various temperatures.

[0028] The amounts of the various components in the cement slurry testsamples and the results of the fluid loss tests are given in Table IIbelow. TABLE II Fluid Loss Test Results Quantity of Fluid Loss SetCement Control Retarding Salt,⁴ Composition Additive, % Additive,³ % byTest Sample Fluid Loss Control by wt. of % by wt. wt. of TemperatureFluid Loss, No. Additive Used Cement of Cement Cement ° F. ml/minutes 1Prior Art¹ 0.4 — —  80 29/30 2 Present Invention² 0.4 — —  80 19/30 3Prior Art¹ 0.6 0.2 — 140 55/25 4 Present Invention² 0.6 0.2 — 140 38/305 Prior Art¹ 0.6 — 5 140  56/4.5 6 Present Invention² 0.6 — 5 140 57/117 Prior Art¹ 0.8 0.4 — 180 55/20 8 Present Invention² 0.8 0.4 — 18045/30

[0029] From Table II it can be seen that the terpolymer fluid losscontrol additive of the present invention provides better fluid losscontrol than the prior art additive.

[0030] Thus, the present invention is well adapted to carry out theobjects and attain the ends and advantages mentioned as well as thosewhich are inherent therein. While numerous changes may be made by thoseskilled in the art, such changes are encompassed within the spirit ofthis invention as defined by the appended claims.

What is claimed is:
 1. A terpolymer fluid loss control additive for usein a well cement composition comprising first, second and third monomerswherein said first monomer is selected from the group consisting of2-acrylamido-2-methylpropane sulfonic acid,2-allyloxy-2-hydroxy-1-propane sulfonic acid and vinylsulfonic acid,said second monomer is selected from the group consisting ofN,N-dimethylacrylamide, acrylamide, N-vinylpyrrolidone, N-vinylacetamideand acrylonitrile and said third monomer is selected from the groupconsisting of C₆ to C₂₂ dimethylaminopropylmethacrylamide bromide,chloride and iodide and C₆ to C₂₂ dimethylaminoethylmethacrylatebromide, chloride and iodide.
 2. The terpolymer fluid loss controladditive of claim 1 wherein said additive has a molecular weight in therange of from about 75,000 to about 300,000.
 3. The terpolymer fluidloss control additive of claim 1 wherein said first monomer is presentin said terpolymer in an amount in the range of from about 50 to about70 mole percent, said second monomer is present in said terpolymer in anamount in the range of from about 30 to about 50 mole percent and saidthird monomer is present in said terpolymer in an amount in the range offrom about 1 to about 10 mole percent.
 4. The terpolymer fluid losscontrol additive of claim 1 wherein said first monomer is present insaid terpolymer in an amount in the range of from about 60 to about 70mole percent, said second monomer is present in said terpolymer in anamount in the range of from about 30 to about 40 mole percent and saidthird monomer is present in said terpolymer in an amount in the range offrom about 1 to about 5 mole percent.
 5. The terpolymer fluid losscontrol additive of claim 1 wherein said terpolymer is comprised of a2-acrylamido-2-methylpropane sulfonic acid first monomer, aN,N-dimethylacrylamide second monomer and a C₆ to C₂₂dimethylaminopropylmethacrylamide bromide, chloride or iodide thirdmonomer.
 6. The terpolymer fluid loss control additive of claim 5wherein said first monomer is present in said terpolymer in an amount inthe range of from about 50 to about 70 mole percent, said second monomeris present in said terpolymer in an amount in the range of from about 30to about 50 mole percent and said third monomer is present in an amountin the range of from about 1 to about 10 mole percent.
 7. The terpolymerfluid loss control additive of claim 1 wherein said terpolymer iscomprised of a 2-acrylamido-2-methylpropane sulfonic acid first monomer,a N,N-dimethylacrylamide second monomer and ahexadecyldimethylaminopropylmethacrylamide bromide third monomer.
 8. Theterpolymer fluid loss control additive of claim 7 wherein said firstmonomer is present in said terpolymer in an amount of about 59.5 molepercent, said second monomer is present in said terpolymer in an amountof about 39.5 mole percent and said third monomer is present in saidterpolymer in an amount of about 1 mole percent.
 9. A terpolymer fluidloss control additive for use in a well cement composition having amolecular weight in the range of from about 75,000 to about 300,000comprising first, second and third monomers wherein said first monomeris present in said terpolymer in an amount in the range of from about 50to about 70 mole percent and is selected from the group consisting of2-acrylamido-2-methylpropane sulfonic acid,2-allyloxy-2-hydroxy-1-propane sulfonic acid and vinylsulfonic acid,said second monomer is present in said terpolymer in an amount in therange of from about 30 to about 50 mole percent and is selected from thegroup consisting of N,N-dimethylacrylamide, acrylamide,N-vinylpyrrolidone, N-vinylacetamide and acrylonitrile and said thirdmonomer is present in said terpolymer in an amount in the range of fromabout 1 to about 10 mole percent and is selected from the groupconsisting of C₆ to C₂₂ dimethylaminopropylmethacrylamide bromide,chloride and iodide and C₆ to C₂₂ dimethy
 10. The terpolymer fluid losscontrol additive of claim 9 wherein said terpolymer is comprised of a2-acrylamido-2-methylpropane sulfonic acid first monomer, aN,N-dimethylacrylamide second monomer and a C₆ to C₂₂dimethylaminopropylmethacrylamide bromide, chloride or iodide thirdmonomer.
 11. The terpolymer fluid loss control additive of claim 9wherein said first monomer is present in said terpolymer in an amount inthe range of from about 60 to about 70 mole percent, said second monomeris present in said terpolymer in an amount in the range of from about 30to about 40 mole percent and said third monomer is present in saidterpolymer in an amount in the range of from about 1 to about 5 molepercent.
 12. The terpolymer fluid loss control additive of claim 9wherein said terpolymer is comprised of a 2-acrylamido-2-methylpropanesulfonic acid first monomer, a N,N-dimethylacrylamide second monomer anda hexadecyldimethylaminopropylmethacrylamide bromide third monomer. 13.The terpolymer fluid loss control additive of claim 12 wherein saidfirst monomer is present in said terpolymer in an amount of about 59.5mole percent, said second monomer is present in said terpolymer in anamount of about 39.5 mole percent and said third monomer is present insaid terpolymer in an amount of about 1 mole percent.
 14. A terpolymerfluid loss control additive for use in a well cement composition havinga molecular weight in the range of from about 75,000 to about 300,000comprising a 2-acrylamido-2-methylpropane sulfonic acid first monomer, aN,N-dimethylacrylamide second monomer and a C₆ to C₂₂dimethylaminopropylmethacrylamide bromide, chloride or iodide thirdmonomer.
 15. The terpolymer fluid loss control additive of claim 14wherein said first monomer is present in said terpolymer in an amount inthe range of from about 50 to about 70 mole percent, said second monomeris present in said terpolymer in an amount in the range of from about 30to about 50 mole percent and said third monomer is present in saidterpolymer in an amount in the range of from about 1 to about 10 molepercent.
 16. The terpolymer fluid loss control additive of claim 14wherein said first monomer is present in said terpolymer in an amount inthe range of from about 60 to about 70 mole percent, said second monomeris present in said terpolymer in an amount in the range of from about 30to about 40 mole percent and said third monomer is present in saidterpolymer in an amount in the range of from about 1 to about 5 molepercent.
 17. The terpolymer fluid loss control additive of claim 14wherein said first monomer is present in said terpolymer in an amount ofabout 59.5 mole percent, said second monomer is present in saidterpolymer in an amount of about 39.5 mole percent and said thirdmonomer is present in said terpolymer in an amount of about 1 molepercent.
 18. A terpolymer fluid loss control additive for use in a wellcement composition having a molecular weight in the range of from about75,000 to about 300,000 comprising a 2-acrylamido-2-methylpropanesulfonic acid first monomer, a N,N-dimethylacrylamide second monomer anda hexadecyldimethylaminopropylmethacrylamide bromide third monomer. 19.The terpolymer fluid loss control additive of claim 18 wherein saidfirst monomer is present in said terpolymer in an amount in the range offrom about 50 to about 70 mole percent, said second monomer is presentin said terpolymer in an amount in the range of from about 30 to about50 mole percent and said third monomer is present in said terpolymer inan amount in the range of from about 1 to about 10 mole percent.
 20. Theterpolymer fluid loss control additive of claim 18 wherein said firstmonomer is present in said terpolymer in an amount in the range of fromabout 60 to about 70 mole percent, said second monomer is present insaid terpolymer in an amount in the range of from about 30 to about 40mole percent and said third monomer is present in said terpolymer in anamount in the range of from about 1 to about 5 mole percent.
 21. Theterpolymer fluid loss control additive of claim 18 wherein said firstmonomer is present in said terpolymer in an a mount of about 59.5mole-percent, said second monomer is present in said terpolymer in anamount of about 39.5 mole percent and said third monomer is present insaid terpolymer in an amount of about 1 mole percent.